1. Field of the Invention
The present invention relates to a suspension apparatus for vehicles capable of changing the characteristics of suspension by controlling the supply and release amounts of hydraulic flow to hydraulic cylinders.
2. Description of the Related Art
A conventional suspension apparatus, an active control suspension apparatus (ACS apparatus) is well known as disclosed in Japanese Kokai No. Hei 3-182826. This ACS apparatus is provided with a hydraulic cylinder between a vehicle body and each wheel, and changes the characteristics of the suspension in accordance with a driving state by independently controlling the fluid flow amount to each hydraulic cylinder with a flow control valve.
In the conventional technique, a vehicle-height signal and vertical acceleration signal are collected on each wheel. The collected signals are passed through a low-pass filter, to extract a bouncing component, pitching component, and rolling component of vehicle movement from the low-pass components, and flow control signals are calculated for the hydraulic cylinders to suppress a movement of the vehicle body on each of bouncing mode, pitching mode, and rolling mode.
The low-pass filter is used in the conventional technique, because if the gain of a relatively high frequency component is not decreased, the control of changing the suspension characteristic is excessively applied to the movement of the vehicle body having a relatively high frequency, resulting in a resonance.
Comfortableness depends on the bouncing mode and pitching mode, and controllability and stability are influenced by the movement on the rolling mode. Accordingly, the suspension control to suppress the rolling movement should have a characteristic which is different from the control to suppress the bouncing movement or the pitching movement.
However, in the above-described conventional technique, an overall height signal (or a vertical G signal) is subjected to the low-pass filter. Therefore, the gain for the rolling component can not be independently changed. Accordingly, a transitional rolling movement of the vehicle body can not be prevented, resulting in a decrease on the controllability and stability.